Resistance to clindamycin (Cc-r) and tetracycline (Tc-r) can be transferred by conjugation in bacteroides. Certain Cc-r strains contain conjugative Cc-r plasmids. The conjugative Tc-r elements and conjugative Tc-r-Cc-r elements are not found on plasmids but appear to be integrated in the Bacteroides chromosome. Clindamycin is the drug of choice for treating anaerobic infections, and the spread of Cc-r among Bacteroides is of clinical concern. The Tc-r conjugal system sometimes co-transfers Cc-r en bloc and can mobilize at least one Cc-r plasmid and several cryptic Bacteroides plasmids. Three of the conjugative Cc-r plasmids contain a transposon, Tn4351, which carries the Cc-r determinant and a *Tc-r determinant that expresses only in aerobically grown E. coli. Tn4351 transposes in both E. coli and Bacteroides. Tn4351 will be used to study the spread of Cc-r to Bacteroides chromosome and to Bacteroides plasmids, especially to any of the cryptic plasmids. The Tc-r system will be characterized, using Tn4351, by the following methods: i) Use Tn4351 insertions into the Tc-r element in Bacteroides to allow cloning in E. coli to determine the size and location of the entire Tc-r element and to subclone and isolate the Tc-r determinant itself. ii) Use Tn4351 transposon mutagenesis to locate the transfer genes of the Tc-r system and to cause auxotrophs in Bacteroides to determine if chromosomal DNA is co-transferred with Tc-r. iii) Use methods similar to those used to isolate Tn4351 to determine if the Tc-r is also on a transposon. iv) Use Tn4351, containing cloned origins of transfer that are recognized by the Tc-r system, inserted into various sites of the Bacteroides chromosome to see if the Tc-r system will initiate transfer of the chromosome at those sites.